Proper and adequate ventilation of attics, roofs, and crawl spaces in commercial and residential structures is very important. Many building code enforcement agencies require that these ventilation systems allow and permit sufficient airflow into and out of attics, roofs, and crawl spaces to prevent ice dams, excessive heating, condensation, mold, and mildew problems due to insufficient airflow. Many building code enforcement agencies also require that these ventilation systems include a metal screen for the purpose of minimizing the intrusion of burning embers and preventing the entry of pests and insects through the ventilation vents.
An example of this type of ventilation system may be found on the typical residential house, where intake vents are commonly located along the soffit area, below the roofline, and exhaust vents are commonly located along the roof ridgeline or on the top of the roof surface itself. When installed properly, these ventilation systems prove to be very valuable. However, these ventilation systems are also a cause of concern as it relates to the unwanted entry of burning embers, ashes, water, and debris, which can enter through the vents in the ventilation system.
During a wildfire, ashes and burning embers are known to be carried away from the fire by the wind. When these ashes and burning embers are blown against a structure such as a house, they can rise up the exterior wall and become pulled into the attic by the airflow which naturally flows into the attic through the intake vents commonly located along the soffit area. In another example, during a hurricane, water and flying debris are known to penetrate common building ventilation systems due to the high winds and pressure differentials which this wind can cause from one side of the structure to the other.
For both wildfires and hurricanes, one can easily understand the problems that these scenarios present. When burning embers enter a structure through common ventilation systems, they can smolder and burn and ignite the structure from the inside, causing significant property loss, as is well documented in numerous fire research studies. Additionally, when water and flying debris are blown into a structure through common ventilation systems, or when pressure differentials become extreme, tremendous damage is likely and the repair costs can be extremely high. This is also well documented in post-hurricane property damage assessments.